Albert, Bernard and Bell’s Theorem

Posted in The Universe and Stuff with tags , , , , , , , , , , on April 15, 2015 by telescoper

You’ve probably all heard of the little logic problem involving the mysterious Cheryl and her friends Albert and Bernard that went viral on the internet recently. I decided not to post about it directly because it’s already been done to death. It did however make me think that if people struggle so much with “ordinary” logic problems of this type its no wonder they are so puzzled by the kind of logical issues raised by quantum mechanics. Hence the motivation of updating a post I did quite a while ago. The question we’ll explore does not concern the date of Cheryl’s birthday but the spin of an electron.

To begin with, let me give a bit of physics background. Spin is a concept of fundamental importance in quantum mechanics, not least because it underlies our most basic theoretical understanding of matter. The standard model of particle physics divides elementary particles into two types, fermions and bosons, according to their spin.  One is tempted to think of  these elementary particles as little cricket balls that can be rotating clockwise or anti-clockwise as they approach an elementary batsman. But, as I hope to explain, quantum spin is not really like classical spin.

Take the electron,  for example. The amount of spin an electron carries is  quantized, so that it always has a magnitude which is ±1/2 (in units of Planck’s constant; all fermions have half-integer spin). In addition, according to quantum mechanics, the orientation of the spin is indeterminate until it is measured. Any particular measurement can only determine the component of spin in one direction. Let’s take as an example the case where the measuring device is sensitive to the z-component, i.e. spin in the vertical direction. The outcome of an experiment on a single electron will lead a definite outcome which might either be “up” or “down” relative to this axis.

However, until one makes a measurement the state of the system is not specified and the outcome is consequently not predictable with certainty; there will be a probability of 50% probability for each possible outcome. We could write the state of the system (expressed by the spin part of its wavefunction  ψ prior to measurement in the form

|ψ> = (|↑> + |↓>)/√2

This gives me an excuse to use  the rather beautiful “bra-ket” notation for the state of a quantum system, originally due to Paul Dirac. The two possibilities are “up” (↑­) and “down” (↓) and they are contained within a “ket” (written |>)which is really just a shorthand for a wavefunction describing that particular aspect of the system. A “bra” would be of the form <|; for the mathematicians this represents the Hermitian conjugate of a ket. The √2 is there to insure that the total probability of the spin being either up or down is 1, remembering that the probability is the square of the wavefunction. When we make a measurement we will get one of these two outcomes, with a 50% probability of each.

At the point of measurement the state changes: if we get “up” it becomes purely |↑>  and if the result is  “down” it becomes |↓>. Either way, the quantum state of the system has changed from a “superposition” state described by the equation above to an “eigenstate” which must be either up or down. This means that all subsequent measurements of the spin in this direction will give the same result: the wave-function has “collapsed” into one particular state. Incidentally, the general term for a two-state quantum system like this is a qubit, and it is the basis of the tentative steps that have been taken towards the construction of a quantum computer.

Notice that what is essential about this is the role of measurement. The collapse of  ψ seems to be an irreversible process, but the wavefunction itself evolves according to the Schrödinger equation, which describes reversible, Hamiltonian changes.  To understand what happens when the state of the wavefunction changes we need an extra level of interpretation beyond what the mathematics of quantum theory itself provides,  because we are generally unable to write down a wave-function that sensibly describes the system plus the measuring apparatus in a single form.

So far this all seems rather similar to the state of a fair coin: it has a 50-50 chance of being heads or tails, but the doubt is resolved when its state is actually observed. Thereafter we know for sure what it is. But this resemblance is only superficial. A coin only has heads or tails, but the spin of an electron doesn’t have to be just up or down. We could rotate our measuring apparatus by 90° and measure the spin to the left (←) or the right (→). In this case we still have to get a result which is a half-integer times Planck’s constant. It will have a 50-50 chance of being left or right that “becomes” one or the other when a measurement is made.

Now comes the real fun. Suppose we do a series of measurements on the same electron. First we start with an electron whose spin we know nothing about. In other words it is in a superposition state like that shown above. We then make a measurement in the vertical direction. Suppose we get the answer “up”. The electron is now in the eigenstate with spin “up”.

We then pass it through another measurement, but this time it measures the spin to the left or the right. The process of selecting the electron to be one with  spin in the “up” direction tells us nothing about whether the horizontal component of its spin is to the left or to the right. Theory thus predicts a 50-50 outcome of this measurement, as is observed experimentally.

Suppose we do such an experiment and establish that the electron’s spin vector is pointing to the left. Now our long-suffering electron passes into a third measurement which this time is again in the vertical direction. You might imagine that since we have already measured this component to be in the up direction, it would be in that direction again this time. In fact, this is not the case. The intervening measurement seems to “reset” the up-down component of the spin; the results of the third measurement are back at square one, with a 50-50 chance of getting up or down.

This is just one example of the kind of irreducible “randomness” that seems to be inherent in quantum theory. However, if you think this is what people mean when they say quantum mechanics is weird, you’re quite mistaken. It gets much weirder than this! So far I have focussed on what happens to the description of single particles when quantum measurements are made. Although there seem to be subtle things going on, it is not really obvious that anything happening is very different from systems in which we simply lack the microscopic information needed to make a prediction with absolute certainty.

At the simplest level, the difference is that quantum mechanics gives us a theory for the wave-function which somehow lies at a more fundamental level of description than the usual way we think of probabilities. Probabilities can be derived mathematically from the wave-function,  but there is more information in ψ than there is in |2; the wave-function is a complex entity whereas the square of its amplitude is entirely real. If one can construct a system of two particles, for example, the resulting wave-function is obtained by superimposing the wave-functions of the individual particles, and probabilities are then obtained by squaring this joint wave-function. This will not, in general, give the same probability distribution as one would get by adding the one-particle probabilities because, for complex entities A and B,

A2+B2 ≠(A+B)2

in general. To put this another way, one can write any complex number in the form a+ib (real part plus imaginary part) or, generally more usefully in physics , as Re, where R is the amplitude and θ  is called the phase. The square of the amplitude gives the probability associated with the wavefunction of a single particle, but in this case the phase information disappears; the truly unique character of quantum physics and how it impacts on probabilies of measurements only reveals itself when the phase information is retained. This generally requires two or more particles to be involved, as the absolute phase of a single-particle state is essentially impossible to measure.

Finding situations where the quantum phase of a wave-function is important is not easy. It seems to be quite easy to disturb quantum systems in such a way that the phase information becomes scrambled, so testing the fundamental aspects of quantum theory requires considerable experimental ingenuity. But it has been done, and the results are astonishing.

Let us think about a very simple example of a two-component system: a pair of electrons. All we care about for the purpose of this experiment is the spin of the electrons so let us write the state of this system in terms of states such as  which I take to mean that the first particle has spin up and the second one has spin down. Suppose we can create this pair of electrons in a state where we know the total spin is zero. The electrons are indistinguishable from each other so until we make a measurement we don’t know which one is spinning up and which one is spinning down. The state of the two-particle system might be this:

|ψ> = (|↑↓> – |↓↑>)/√2

squaring this up would give a 50% probability of “particle one” being up and “particle two” being down and 50% for the contrary arrangement. This doesn’t look too different from the example I discussed above, but this duplex state exhibits a bizarre phenomenon known as quantum entanglement.

Suppose we start the system out in this state and then separate the two electrons without disturbing their spin states. Before making a measurement we really can’t say what the spins of the individual particles are: they are in a mixed state that is neither up nor down but a combination of the two possibilities. When they’re up, they’re up. When they’re down, they’re down. But when they’re only half-way up they’re in an entangled state.

If one of them passes through a vertical spin-measuring device we will then know that particle is definitely spin-up or definitely spin-down. Since we know the total spin of the pair is zero, then we can immediately deduce that the other one must be spinning in the opposite direction because we’re not allowed to violate the law of conservation of angular momentum: if Particle 1 turns out to be spin-up, Particle 2  must be spin-down, and vice versa. It is known experimentally that passing two electrons through identical spin-measuring gadgets gives  results consistent with this reasoning. So far there’s nothing so very strange in this.

The problem with entanglement lies in understanding what happens in reality when a measurement is done. Suppose we have two observers, Albert and Bernard, who are bored with Cheryl’s little games and have decided to do something interesting with their lives by becoming physicists. Each is equipped with a device that can measure the spin of an electron in any direction they choose. Particle 1 emerges from the source and travels towards Albert whereas particle 2 travels in Bernard’s direction. Before any measurement, the system is in an entangled superposition state. Suppose Albert decides to measure the spin of electron 1 in the z-direction and finds it spinning up. Immediately, the wave-function for electron 2 collapses into the down direction. If Albert had instead decided to measure spin in the left-right direction and found it “left” similar collapse would have occurred for particle 2, but this time putting it in the “right” direction.

Whatever Albert does, the result of any corresponding measurement made by Bernard has a definite outcome – the opposite to Alberts result. So Albert’s decision whether to make a measurement up-down or left-right instantaneously transmits itself to Bernard who will find a consistent answer, if he makes the same measurement as Albert.

If, on the other hand, Albert makes an up-down measurement but Bernard measures left-right then Albert’s answer has no effect on Bernard, who has a 50% chance of getting “left” and 50% chance of getting right. The point is that whatever Albert decides to do, it has an immediate effect on the wave-function at ’s position; the collapse of the wave-function induced by Albert immediately collapses the state measured by Bernard. How can particle 1 and particle 2 communicate in this way?

This riddle is the core of a thought experiment by Einstein, Podolsky and Rosen in 1935 which has deep implications for the nature of the information that is supplied by quantum mechanics. The essence of the EPR paradox is that each of the two particles – even if they are separated by huge distances – seems to know exactly what the other one is doing. Einstein called this “spooky action at a distance” and went on to point out that this type of thing simply could not happen in the usual calculus of random variables. His argument was later tightened considerably by John Bell in a form now known as Bell’s theorem.

To see how Bell’s theorem works, consider the following roughly analagous situation. Suppose we have two suspects in prison, say Albert and Bernard (presumably Cheryl grassed them up and has been granted immunity from prosecution). The  two are taken apart to separate cells for individual questioning. We can allow them to use notes, electronic organizers, tablets of stone or anything to help them remember any agreed strategy they have concocted, but they are not allowed to communicate with each other once the interrogation has started. Each question they are asked has only two possible answers – “yes” or “no” – and there are only three possible questions. We can assume the questions are asked independently and in a random order to the two suspects.

When the questioning is over, the interrogators find that whenever they asked the same question, Albert and Bernard always gave the same answer, but when the question was different they only gave the same answer 25% of the time. What can the interrogators conclude?

The answer is that Albert and Bernard must be cheating. Either they have seen the question list ahead of time or are able to communicate with each other without the interrogator’s knowledge. If they always give the same answer when asked the same question, they must have agreed on answers to all three questions in advance. But when they are asked different questions then, because each question has only two possible responses, by following this strategy it must turn out that at least two of the three prepared answers – and possibly all of them – must be the same for both Albert and Bernard. This puts a lower limit on the probability of them giving the same answer to different questions. I’ll leave it as an exercise to the reader to show that the probability of coincident answers to different questions in this case must be at least 1/3.

This a simple illustration of what in quantum mechanics is known as a Bell inequality. Albert and Bernard can only keep the number of such false agreements down to the measured level of 25% by cheating.

This example is directly analogous to the behaviour of the entangled quantum state described above under repeated interrogations about its spin in three different directions. The result of each measurement can only be either “yes” or “no”. Each individual answer (for each particle) is equally probable in this case; the same question always produces the same answer for both particles, but the probability of agreement for two different questions is indeed ¼ and not larger as would be expected if the answers were random. For example one could ask particle 1 “are you spinning up” and particle 2 “are you spinning to the right”? The probability of both producing an answer “yes” is 25% according to quantum theory but would be higher if the particles weren’t cheating in some way.

Probably the most famous experiment of this type was done in the 1980s, by Alain Aspect and collaborators, involving entangled pairs of polarized photons (which are bosons), rather than electrons, primarily because these are easier to prepare.

The implications of quantum entanglement greatly troubled Einstein long before the EPR paradox. Indeed the interpretation of single-particle quantum measurement (which has no entanglement) was already troublesome. Just exactly how does the wave-function relate to the particle? What can one really say about the state of the particle before a measurement is made? What really happens when a wave-function collapses? These questions take us into philosophical territory that I have set foot in already; the difficult relationship between epistemological and ontological uses of probability theory.

Thanks largely to the influence of Niels Bohr, in the relatively early stages of quantum theory a standard approach to this question was adopted. In what became known as the  Copenhagen interpretation of quantum mechanics, the collapse of the wave-function as a result of measurement represents a real change in the physical state of the system. Before the measurement, an electron really is neither spinning up nor spinning down but in a kind of quantum purgatory. After a measurement it is released from limbo and becomes definitely something. What collapses the wave-function is something unspecified to do with the interaction of the particle with the measuring apparatus or, in some extreme versions of this doctrine, the intervention of human consciousness.

I find it amazing that such a view could have been held so seriously by so many highly intelligent people. Schrödinger hated this concept so much that he invented a thought-experiment of his own to poke fun at it. This is the famous “Schrödinger’s cat” paradox.

In a closed box there is a cat. Attached to the box is a device which releases poison into the box when triggered by a quantum-mechanical event, such as radiation produced by the decay of a radioactive substance. One can’t tell from the outside whether the poison has been released or not, so one doesn’t know whether the cat is alive or dead. When one opens the box, one learns the truth. Whether the cat has collapsed or not, the wave-function certainly does. At this point one is effectively making a quantum measurement so the wave-function of the cat is either “dead” or “alive” but before opening the box it must be in a superposition state. But do we really think the cat is neither dead nor alive? Isn’t it certainly one or the other, but that our lack of information prevents us from knowing which? And if this is true for a macroscopic object such as a cat, why can’t it be true for a microscopic system, such as that involving just a pair of electrons?

As I learned at a talk a while ago by the Nobel prize-winning physicist Tony Leggett – who has been collecting data on this  – most physicists think Schrödinger’s cat is definitely alive or dead before the box is opened. However, most physicists don’t believe that an electron definitely spins either up or down before a measurement is made. But where does one draw the line between the microscopic and macroscopic descriptions of reality? If quantum mechanics works for 1 particle, does it work also for 10, 1000? Or, for that matter, 1023?

Most modern physicists eschew the Copenhagen interpretation in favour of one or other of two modern interpretations. One involves the concept of quantum decoherence, which is basically the idea that the phase information that is crucial to the underlying logic of quantum theory can be destroyed by the interaction of a microscopic system with one of larger size. In effect, this hides the quantum nature of macroscopic systems and allows us to use a more classical description for complicated objects. This certainly happens in practice, but this idea seems to me merely to defer the problem of interpretation rather than solve it. The fact that a large and complex system makes tends to hide its quantum nature from us does not in itself give us the right to have a different interpretations of the wave-function for big things and for small things.

Another trendy way to think about quantum theory is the so-called Many-Worlds interpretation. This asserts that our Universe comprises an ensemble – sometimes called a multiverse – and  probabilities are defined over this ensemble. In effect when an electron leaves its source it travels through infinitely many paths in this ensemble of possible worlds, interfering with itself on the way. We live in just one slice of the multiverse so at the end we perceive the electron winding up at just one point on our screen. Part of this is to some extent excusable, because many scientists still believe that one has to have an ensemble in order to have a well-defined probability theory. If one adopts a more sensible interpretation of probability then this is not actually necessary; probability does not have to be interpreted in terms of frequencies. But the many-worlds brigade goes even further than this. They assert that these parallel universes are real. What this means is not completely clear, as one can never visit parallel universes other than our own …

It seems to me that none of these interpretations is at all satisfactory and, in the gap left by the failure to find a sensible way to understand “quantum reality”, there has grown a pathological industry of pseudo-scientific gobbledegook. Claims that entanglement is consistent with telepathy, that parallel universes are scientific truths, that consciousness is a quantum phenomena abound in the New Age sections of bookshops but have no rational foundation. Physicists may complain about this, but they have only themselves to blame.

But there is one remaining possibility for an interpretation of that has been unfairly neglected by quantum theorists despite – or perhaps because of – the fact that is the closest of all to commonsense. This view that quantum mechanics is just an incomplete theory, and the reason it produces only a probabilistic description is that does not provide sufficient information to make definite predictions. This line of reasoning has a distinguished pedigree, but fell out of favour after the arrival of Bell’s theorem and related issues. Early ideas on this theme revolved around the idea that particles could carry “hidden variables” whose behaviour we could not predict because our fundamental description is inadequate. In other words two apparently identical electrons are not really identical; something we cannot directly measure marks them apart. If this works then we can simply use only probability theory to deal with inferences made on the basis of information that’s not sufficient for absolute certainty.

After Bell’s work, however, it became clear that these hidden variables must possess a very peculiar property if they are to describe out quantum world. The property of entanglement requires the hidden variables to be non-local. In other words, two electrons must be able to communicate their values faster than the speed of light. Putting this conclusion together with relativity leads one to deduce that the chain of cause and effect must break down: hidden variables are therefore acausal. This is such an unpalatable idea that it seems to many physicists to be even worse than the alternatives, but to me it seems entirely plausible that the causal structure of space-time must break down at some level. On the other hand, not all “incomplete” interpretations of quantum theory involve hidden variables.

One can think of this category of interpretation as involving an epistemological view of quantum mechanics. The probabilistic nature of the theory has, in some sense, a subjective origin. It represents deficiencies in our state of knowledge. The alternative Copenhagen and Many-Worlds views I discussed above differ greatly from each other, but each is characterized by the mistaken desire to put quantum mechanics – and, therefore, probability –  in the realm of ontology.

The idea that quantum mechanics might be incomplete  (or even just fundamentally “wrong”) does not seem to me to be all that radical. Although it has been very successful, there are sufficiently many problems of interpretation associated with it that perhaps it will eventually be replaced by something more fundamental, or at least different. Surprisingly, this is a somewhat heretical view among physicists: most, including several Nobel laureates, seem to think that quantum theory is unquestionably the most complete description of nature we will ever obtain. That may be true, of course. But if we never look any deeper we will certainly never know…

With the gradual re-emergence of Bayesian approaches in other branches of physics a number of important steps have been taken towards the construction of a truly inductive interpretation of quantum mechanics. This programme sets out to understand  probability in terms of the “degree of belief” that characterizes Bayesian probabilities. Recently, Christopher Fuchs, amongst others, has shown that, contrary to popular myth, the role of probability in quantum mechanics can indeed be understood in this way and, moreover, that a theory in which quantum states are states of knowledge rather than states of reality is complete and well-defined. I am not claiming that this argument is settled, but this approach seems to me by far the most compelling and it is a pity more people aren’t following it up…


Spring – Edna St Vincent Millay

Posted in Poetry with tags , , , on April 15, 2015 by telescoper

To what purpose, April, do you return again?
Beauty is not enough.
You can no longer quiet me with the redness
Of little leaves opening stickily.
I know what I know.
The sun is hot on my neck as I observe
The spikes of the crocus.
The smell of the earth is good.
It is apparent that there is no death.
But what does that signify?
Not only under ground are the brains of men
Eaten by maggots.
Life in itself
Is nothing,
An empty cup, a flight of uncarpeted stairs.
It is not enough that yearly, down this hill,
April
Comes like an idiot, babbling and strewing flowers.

by Edna St Vincent Millay (1892-1950)

Dark Matter from the Dark Energy Survey

Posted in The Universe and Stuff with tags , , , on April 14, 2015 by telescoper

I’m a bit late onto this story which has already been quite active in the media today, and has generated an associated flurry of activity on social media, but I thought it was still worth passing it on via the medium of this blog. The Dark Energy Survey has just released a number of papers onto the arXiv, the most interesting of which (to me) is entitled Wide-Field Lensing Mass Maps from DES Science Verification Data. The abstract reads as follows (the link was added by me):

Weak gravitational lensing allows one to reconstruct the spatial distribution of the projected mass density across the sky. These “mass maps” provide a powerful tool for studying cosmology as they probe both luminous and dark matter. In this paper, we present a weak lensing mass map reconstructed from shear measurements in a 139 deg^2 area from the Dark Energy Survey (DES) Science Verification (SV) data overlapping with the South Pole Telescope survey. We compare the distribution of mass with that of the foreground distribution of galaxies and clusters. The overdensities in the reconstructed map correlate well with the distribution of optically detected clusters. Cross-correlating the mass map with the foreground galaxies from the same DES SV data gives results consistent with mock catalogs that include the primary sources of statistical uncertainties in the galaxy, lensing, and photo-z catalogs. The statistical significance of the cross-correlation is at the 6.8 sigma level with 20 arcminute smoothing. A major goal of this study is to investigate systematic effects arising from a variety of sources, including PSF and photo-z uncertainties. We make maps derived from twenty variables that may characterize systematics and find the principal components. We find that the contribution of systematics to the lensing mass maps is generally within measurement uncertainties. We test and validate our results with mock catalogs from N-body simulations. In this work, we analyze less than 3% of the final area that will be mapped by the DES; the tools and analysis techniques developed in this paper can be applied to forthcoming larger datasets from the survey.

This is by no means a final result from the Dark Energy Survey, as it was basically put together in order to test the telescope, but it is interesting from the point of view that it represents a kind of proof of concept. Here is one of the key figures from the paper which shows a reconstruction of the mass distribution of the Universe (dominated by dark matter) obtained indirectly by the Dark Energy Survey using distortions of galaxy images produced by gravitational lensing by foreground objects, onto which the positions of large galaxy clusters seen in direct observations have been plotted. Although this is just a small part of the planned DES study (it covers only 0.4% of the sky) it does seem to indicate that the strong concentrations of dark matter (red) do corrrelate with the positions of concentrations of galaxy clusters.

DES_MAP

It all seems to work, so hopefully we can look forward to lots of interesting science results in future!

P.S. When I first saw the map it looked like a map of the North of England Midlands and I was surprised to see that the survey showed such strong support for the Greens…

Local Politics – Brighton Kemptown

Posted in Brighton, Politics with tags , , on April 13, 2015 by telescoper

I haven’t posted much about the forthcoming General Election but I couldn’t resist making a short comment about the situation here in Brighton & Hov, which is actually quite interesting. The three constituencies in the city are all marginal: Hove, Brighton Pavilion, and Brighton Kemptown. All of these were Conservative strongholds until 1997, when they all fell to the Labour party which held them until the last General Election 2010. Hove and Brighton fell to the Conservatives in 2010 while Brighton Pavilion was taken by the UK’s only Green MP, Caroline Lucas. Much of the media attention in Brighton is focussing on the latter seat, where (surprisingly to my mind), Caroline Lucas seems set to retain her place in the House of Commons having apparently succeeded in her campaign of distancing herself from the local Green Party’s abject performance in running Brighton and Hove City Council.

I am currently living in Brighton Kemptown, a two-way marginal in which the Labour candidate (Nancy Platts) is fighting the incumbent Conservative (Simon Kirby). The seat encompasses the eastern part of Brighton and the semi-rural suburbs and villages stretching out to the east of the seat. At its western end it includes Queen`s Park ward, the centre of Brighton`s vibrant gay community, then Kemptown, the council estates of Whitehawk and Moulscoomb and then, beyond the racecourse, more affluent and genteel coastal villages like Woodingdean, Saltdean and the town of Peacehaven. At the north of the seat is Brighton University`s Falmer campus – despite Moulscoomb itself being in the constituency, Moulscoomb campus lies just over the boundary marked by the A27  in Brighton Pavilion. The University of Sussex, where I work, also has a campus at Falmer, but it is also in Brighton Pavilion.

Here is a map showing the constituency boundaries:

Brighton_Kemptown

I often get the No. 23 bus home from work in the evenings. The route of this bus takes it down the A27 to Elm Grove, where it turns left up the hill into Elm Grove which runs uphill into Hanover, which is (more-or-less) that segment at the Western boundary of Brighton Kemptown that has been eaten into by Brighton Pavilion. The bus then turns right and travels south taking it into Queen’s Park and then left again to take it along towards the Marina (the bit that sticks out into the sea).

I know it’s not a very scientific guide to the likely election result, but it is noticeable that the posters showing in the windows in the houses of the Hanover salient of Brighton Pavilion are almost exclusively for Caroline Lucas while those along the rest of journey in Kemptown are almost exclusively for Nancy Platts. It’s a remarkably sudden transition that coincides with the constituency boundary in fact. I’m not sure how much it is reasonable to infer from this observation, but I’d say based on other evidence that Caroline Lucas will probably hold Brighton Pavilion and Nancy Platts will be the next Member of Parliament for Brighton Kemptown.

But of course I could be wrong.

Last Call for Cosmology Talks at NAM 2015!

Posted in The Universe and Stuff with tags , on April 13, 2015 by telescoper

Just a quick post about this year’s forthcoming Royal Astronomical Society National Astronomy Meeting, which will be taking place at the splendid Venue Cymru conference centre, Llandudno, North Wales, from Sunday 5th July to Thursday 9th July 2015. I’m on the Scientific Organizing Committee for NAM 2015 and as such I’ll be organizing a part of this meeting, namely a couple of sessions on Cosmology under the title Cosmology Beyond the Standard Model, with the following description.

Recent observations, particularly those from the Planck satellite, have provided strong empirical foundations for a standard cosmological model that is based on Einstein’s general theory of relativity and which describes a universe which is homogeneous and isotropic on large scales and which is dominated by dark energy and matter components. This session will explore theoretical and observational challenges to this standard picture, including modified gravity theories, models with large-scale inhomogeneity and/or anisotropy, and alternative forms of matter-energy. The aim will be to both take stock of the evidence for, and stimulate further investigation of, physics beyond the standard model.

The deadline for submitting abstracts for this and other sessions was originally 1st April, but this has been extended until 14th April (i.e. tomorrow). The cosmology sessions are shaping up to be very interesting indeed, but I might be able to squeeze in one or two more talks. If you’ve been prevaricating about submitting a proposal, then please get your finger out and visit the NAM2015 website right now. This is your last chance!

NAM is a particularly good opportunity for younger researchers – PhD students and postdocs – to present their work to a big audience so I particularly encourage such persons to submit abstracts. Would more senior readers please pass this message on to anyone they think might want to give a talk?

If you have any questions please feel free to use the comments box (or contact me privately).

Uncovered cricket pitches: the degree syllabus

Posted in Cricket, Education with tags , , , on April 12, 2015 by telescoper

telescoper:

Interesting proposal from Keith Flett for a new module for university students on uncovered pitches in cricket. My own view is that the syllabus on this fascinating subject should also discuss the physics behind the variable bounce and turn such pitches produced.

Originally posted on Kmflett's Blog:

Uncovered pitches: the degree Syllabus

cricket pitch

In its issue of 21st January 2015 the Times Higher reported that the University of the Highlands and Islands is to offer a degree in professional golf.

I responded that it was surely time to offer a degree in cricket too (28th January 2015).

Subjects covered could well include the Laws of Cricket, the history of the game (a very substantial subject in itself) Gentleman v Players and class in cricket, Race and Imperialism in cricket. There is also scope for modules on cricket management and coaching and like many degrees no doubt students would select those areas of most relevance to their interests and future careers.

One area that must certainly should be covered however is that of Uncovered Pitches.  To mark the start of the English cricket season and indeed the start at nearly the same time of a West Indies…

View original 201 more words

A Birthday Message to Donald Lynden-Bell

Posted in The Universe and Stuff with tags , on April 12, 2015 by telescoper

On Friday being the second Friday of the month of April I went up to London for the regular Open Meeting of the Royal Astronomical Society and afterwards to dinner with the RAS Club. Unusually for club dinners, we were provided with champagne before the toasts but it was a while before I realized why. A distinguished member and indeed former President of the club, Prof. Donald Lynden-Bell, had recently celebrated his eightieth birthday and we were all invited to drink his health.

Donald is an amazing character, not least because he hasn’t changed a bit since I first met him over thirty years ago when he was lecturer for one of the courses I took in the first year. His research has spanned an enormous breadth of subjects, from theoretical topics in classical and quantum physics to astrophysics and cosmology, including data analysis. Anyway, it was great that he was there to receive the toast in person. I’ll take the opportunity here to say a more public Happy Birthday!

On the way home I posted on Facebook that Donald had just celebrated his eightieth birthday. One of my astronomer friends, Manuela Magliocchetti, posted a charming comment about him that I’m sharing here (below) publicly in a slightly edited form, with her permission. By the way, in the interest of full disclosure, I should point out that I subsequently had the honour to be the External Examiner for Manuela’s PhD…

–o–

I just learnt that today from Peter there were celebrations at the RAS Dining Club for the 80th birthday of Professor Donald Lynden-Bell. Since I basically owe my scientific carrier to him, I thought I’d  thank him publicly now.

It was summer 1995 and I had pestered my undergraduate supervisor to send me to Cambridge to attend the conference on Gravitational Dynamics that had been organized for the 60th birthday of Donald (gee, already 20 years ago!), since all my undergrad thesis was on some evidence of a phenomenon (gravothermal catastrophe) that he first theorized in a breakthrough paper published in 1968 that by then I knew by heart. So he definitely was my scientific hero.

At the end of the conference I knocked at his office door to ask him whether it was possible for me to apply for a PhD position at Cambridge. He let me in, but did not even allow me to start talking. Instead he started asking me about the thesis work I had done, since in Italy everyone in Physics has to produce some original work in order to be awarded the undegraduate degree. He had me writing on his blackboard for about an hour (which felt like centuries to me) about all my results, asking genuinely interested questions, discussing, and in some bits  criticizing my work. He was very pushy (as I learned later, this  was his style) and was talking oh-so-very fast.

I was soo unsettled and scared and not even sure I was understanding all his points correctly: my English was so basic… After all this torture, he suddently stopped and, with his slightly squeaky voice, went:” So, why are you here?” I very humbly answered that it was to have information on how to apply to Cambridge for a PhD position. He then looked at me, then at the blackboard, then at me again and told me what I wrote on the blackboard indeed was PhD work. I answered that no, it was just undergraduate work. At that point he jumped off his chair, grabbed my arm and dragged me to the secretary of the Isaac Newton Scholarship, introducing me to her and telling her that I would be applying for both a PhD position at the Institute of Astronomy at University of Cambridge and for the scholarship. So I did apply, and in the end got both and found myself thrown in that fantastically stimulating environment which is Cambridge and the IoA.

Thank you so much Donald! Forever grateful. Without you all this and what happened next, including my present job and career and even my kids, since I met their (astronomer) dad over there, would not have been possible!

 

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